KR20230087081A - Super absorbent polymer and preparation method thereof - Google Patents

Abstract

The present invention relates to a superabsorbent polymer and a method for producing the same and, more specifically, to a superabsorbent polymer containing two or more types of hydrophobic materials and having improved tactile feel after swelling without deterioration in absorbent performance, and a method for producing the same. The superabsorbent polymer comprises: superabsorbent polymer resin particles having a base resin including a first cross-linked polymer of a water-soluble ethylenically unsaturated monomer having at least partially neutralized acidic group, and a surface cross-linked layer including a second cross-linked polymer in which the first cross-linked polymer is additionally cross-linked through a surface cross linking agent; and two or more types of hydrophobic substances containing a linear or branched hydrocarbon group having 11 or more carbon atoms.

Description

Super absorbent polymer and its manufacturing method {SUPER ABSORBENT POLYMER AND PREPARATION METHOD THEREOF}

The present invention relates to a superabsorbent polymer and a method for preparing the same. More specifically, it relates to a super absorbent polymer containing two or more types of hydrophobic materials and having an improved tactile feel after swelling without deterioration in absorbent performance and a manufacturing method thereof.

Super Absorbent Polymer (SAP) is a synthetic high-molecular substance that has the ability to absorb moisture 500 to 1,000 times its own weight. Material), etc., are named by different names. The superabsorbent polymer as described above has begun to be put into practical use as a sanitary tool, and is currently widely used as a material for gardening soil remediation agents, civil engineering and construction waterstop materials, seedling sheets, freshness retainers in the field of food distribution, and steaming. .

These superabsorbent polymers are widely used in sanitary materials such as diapers and sanitary napkins. In the sanitary material, it is common that the superabsorbent polymer is included in a spread state in the pulp. However, in recent years, efforts have been made to provide sanitary materials such as diapers with a thinner thickness, and as part of this, the content of pulp is reduced or, furthermore, so-called pulpless diapers in which pulp is not used at all. Development is actively progressing.

As described above, in the case of a sanitary material in which the pulp content is reduced or pulp is not used, the super absorbent polymer is included in a relatively high ratio, so that the super absorbent polymer particles are inevitably included in multiple layers in the sanitary material. In order for the entire superabsorbent polymer particles included in multiple layers to more efficiently absorb a large amount of liquid such as urine, the superabsorbent polymer basically needs to exhibit high absorption performance as well as a fast absorption rate.

Furthermore, as the production of ultra-thin sanitary products increases, it is becoming important whether or not the sanitary material can exhibit an unpleasant touch while maintaining a dry state for a long time after absorbing liquid such as urine. In this regard, conventionally, attempts have been made to improve the dryness and touch of the surface of the super absorbent polymer by forming large and small pores on the surface of the super absorbent polymer so that liquid can be quickly absorbed. As the gel strength of the absorbent polymer is weakened, the liquid permeability of the gel is lowered, and as a result, there has been a problem that the absorption rate and diffusion area of the sanitary material are lowered.

Accordingly, there is a continuous demand for the development of a technology that allows the swollen super absorbent polymer to have an improved touch by absorbing liquid such as urine while maintaining the absorption rate and performance of the super absorbent polymer.

Accordingly, the present invention relates to a superabsorbent polymer having improved tactile feel after swelling without deterioration in absorbent performance by including two or more kinds of hydrophobic materials having a specific structure and a manufacturing method thereof.

In order to solve the above problems, the present invention,

A base resin comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized, and a second crosslinked polymer formed on the base resin and further crosslinked with a surface crosslinking agent. superabsorbent polymer particles including a surface crosslinking layer containing a crosslinked polymer; and

Contains two or more hydrophobic substances containing a linear or branched hydrocarbon group having 11 or more carbon atoms,

The hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters, providing a superabsorbent polymer:

In addition, the present invention,

forming a water-containing gel polymer by cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal cross-linking agent and a polymerization initiator (Step 1);

drying and pulverizing the water-containing gel polymer to prepare a base resin (step 2); and

Forming a surface crosslinking layer on at least a part of the surface of the base resin by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent and two or more kinds of hydrophobic materials including a linear or branched hydrocarbon group having 11 or more carbon atoms. (step 3),

The hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters,

A method for preparing a superabsorbent polymer is provided.

According to the super absorbent polymer and method for preparing the super absorbent polymer of the present invention, at least two hydrophobic materials having a specific structure are added to the base resin surface crosslinking step to hydrophobize a part of the super absorbent polymer surface, thereby swelling the super absorbent polymer without deteriorating the absorbent performance. It can improve the tactile sensation.

Terms used in this specification are only used to describe exemplary embodiments, and are not intended to limit the present invention. Singular expressions include plural expressions unless the context clearly dictates otherwise. In this specification, terms such as "comprise", "comprise" or "having" are intended to indicate that there is an embodied feature, step, component, or combination thereof, but one or more other features or steps; It should be understood that the presence or addition of components, or combinations thereof, is not previously excluded.

Since the present invention can have various changes and various forms, specific embodiments will be exemplified and described in detail below. However, it should be understood that this is not intended to limit the present invention to the specific disclosed form, and includes all modifications, equivalents, and substitutes included in the spirit and scope of the present invention.

The terminology used herein is only intended to refer to specific embodiments and is not intended to limit the present invention. And, as used herein, the singular forms also include the plural forms unless the phrases clearly indicate the opposite.

The term "polymer" or "polymer" used in the specification of the present invention means a state in which water-soluble ethylenically unsaturated monomers are polymerized, and may cover all moisture content ranges or particle size ranges. Among the polymers, polymers in a state after polymerization and before drying and having a moisture content (moisture content) of about 40% by weight or more may be referred to as hydrogel polymers, and particles obtained by pulverizing and drying such hydrogel polymers may be referred to as crosslinked polymers. there is.

Also, the term “superabsorbent polymer particles” refers to a particulate material including a crosslinked polymer obtained by polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group and at least partially neutralizing the acidic group and crosslinking by an internal crosslinking agent.

Also, the term “superabsorbent polymer”, depending on the context, refers to a crosslinked polymer in which a water-soluble ethylenically unsaturated monomer containing an acidic group and at least a portion of which is neutralized is polymerized, or a powder made of superabsorbent polymer particles in which the crosslinked polymer is pulverized (Powder) type base resin, or a product suitable for commercialization through additional processes such as surface crosslinking, fine powder reassembly, drying, pulverization, classification, etc. to the crosslinked polymer or the base resin It is used to cover all. Accordingly, the term “super absorbent polymer” may be interpreted as including a composition including the super absorbent polymer, that is, a plurality of super absorbent polymer particles.

In recent years, as the demand for sanitary materials, especially disposable ultra-thin diapers with a thin thickness, has increased, the tactile feel of the diaper surface after absorbing urine has become an important criterion for evaluating the characteristics of the diaper. Accordingly, when the present inventors use a mixture of two or more types of hydrophobic materials containing a linear or branched hydrocarbon group having 11 or more carbon atoms in the base resin surface treatment step, at least a part of the surface of the super absorbent polymer is hydrophobic, so that the super absorbent polymer becomes urine. After absorbing and swelling, it was confirmed that it exhibits improved tactile sensation, and the present invention was completed.

Specifically, the hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters. Such a hydrophobic material includes a hydrophobic functional group called a linear or branched hydrocarbon group having 11 or more carbon atoms, wherein the hydrocarbon group can be understood to encompass all of an alkyl group, an alkenyl group, and an alkynyl group. In addition, the hydrophobic material preferably includes at least one linear or branched hydrocarbon group having 11 or more and 20 or less carbon atoms in the compound. If the carbon number of the longest chain hydrocarbon group included in the hydrophobic material is less than 11, there is a problem that the surface of the superabsorbent polymer cannot be sufficiently hydrophobic because the chain length is short, and the longest chain hydrocarbon group included in the hydrophobic material When the number of carbon atoms exceeds 20, the mobility of the hydrophobic material may be reduced, so that it may not be effectively mixed with the base resin, and the cost of the hydrophobic material may increase, resulting in an increase in manufacturing cost.

For example, the hydrophobic material may include a linear alkyl having 11 to 20 carbon atoms. More specifically, for example, the hydrophobic material is n-undecanyl, n-dodecanyl, n-tridecanyl, n-tetradecanyl, n-pentadecanyl, n-hexadecanyl, n-heptadecanyl , n-octadecanyl, n-nonadecanyl, or n-icosanil.

In addition, the hydrophobic material may further include a hydrophilic functional group such as a hydroxyl group and an ester group in addition to the aforementioned hydrophobic functional group such as a linear or branched hydrocarbon group having 11 or more carbon atoms. Since the water-soluble ethylenically unsaturated monomer contains an acidic group (-COOH) and/or a neutralized acidic group ( ^-COO- ), the surface of the superabsorbent polymer particle containing the crosslinked polymer of the water-soluble ethylenically unsaturated monomer does not participate in polymerization. A large amount of hydrophilic moieties due to remaining acidic groups (-COOH) and/or neutralized acidic groups ( ^-COO- ) are present. Therefore, since the hydrophilic functional group included in the hydrophobic material is adsorbed to the hydrophilic portion remaining on the surface of the super absorbent polymer, the surface of the super absorbent polymer to which the hydrophobic material is adsorbed is linear with 11 or more carbon atoms located at the other end of the hydrophobic material. Alternatively, hydrophobicity is exhibited by a hydrophobic functional group such as a branched hydrocarbon group. Accordingly, a part of the surface of the super absorbent polymer is hydrophobic, so that the tactile sensation may be improved even after the super absorbent polymer is swollen.

Hereinafter, a superabsorbent polymer and a manufacturing method thereof will be described in more detail according to specific embodiments of the present invention.

super absorbent polymer

A base resin comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized, and a second crosslinked polymer formed on the base resin and further crosslinked with a surface crosslinking agent. superabsorbent polymer particles including a surface crosslinking layer containing a crosslinked polymer; And two or more hydrophobic materials containing a linear or branched hydrocarbon group having 11 or more carbon atoms;

The hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters, and polyoxyethylene sorbitan fatty acid esters.

Hereinafter, the superabsorbent polymer of one embodiment will be described in more detail for each component.

The superabsorbent polymer of one embodiment is formed on a base resin including a first crosslinked polymer of a plurality of water-soluble ethylenically unsaturated monomers having at least partially neutralized acidic groups and an internal crosslinking agent, and the base resin, It includes superabsorbent polymer particles including a surface crosslinking layer including a second crosslinked polymer in which the first crosslinked polymer is additionally crosslinked with a surface crosslinking agent. At this time, the first crosslinked polymer is obtained by crosslinking polymerization of the water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal crosslinking agent, and the main chains formed by polymerization of the monomers are crosslinked by the internal crosslinking agent It has a three-dimensional network structure of the form. As such, when the crosslinked polymer has a three-dimensional network structure in which the main chains formed by polymerization of the monomers are crosslinked by the internal crosslinking agent, compared to a case where the crosslinked polymer has a two-dimensional linear structure not additionally crosslinked by the internal crosslinking agent. The water retention capacity and absorbency under pressure, which are all physical properties of the superabsorbent polymer, can be remarkably improved.

The water-soluble ethylenically unsaturated monomer may be any monomer commonly used in the preparation of super absorbent polymers. As a non-limiting example, the water-soluble ethylenically unsaturated monomer may be a compound represented by Formula 2 below:

[Formula 2]

R-COOM'

In Formula 2,

R is an alkenyl group having 2 to 5 carbon atoms containing an unsaturated bond,

M' is a hydrogen atom, a monovalent or divalent metal, an ammonium group, or an organic amine salt.

Preferably, the monomer may be at least one selected from the group consisting of (meth)acrylic acid and monovalent (alkali) metal salts, divalent metal salts, ammonium salts, and organic amine salts of these acids.

As such, when (meth)acrylic acid and/or its salt is used as the water-soluble ethylenically unsaturated monomer, it is advantageous to obtain a superabsorbent polymer with improved water absorbency. In addition, the monomers include maleic anhydride, fumaric acid, crotonic acid, itaconic acid, 2-acryloylethanesulfonic acid, 2-methacryloylethanesulfonic acid, 2-(meth)acryloylpropanesulfonic acid or 2-(meth)acryloylethanesulfonic acid. ) Acrylamide-2-methyl propane sulfonic acid, (meth)acrylamide, N-substituted (meth)acrylate, 2-hydroxyethyl (meth)acrylate, 2-hydroxypropyl (meth)acrylate, methoxypolyethylene Glycol (meth)acrylate, polyethylene glycol (meth)acrylate, (N,N)-dimethylaminoethyl (meth)acrylate, (N,N)-dimethylaminopropyl (meth)acrylamide and the like can be used.

Here, the water-soluble ethylenically unsaturated monomer has an acidic group, and at least some of the acidic groups may be neutralized by a neutralizing agent. Specifically, in the step of mixing the water-soluble ethylenically unsaturated monomer having an acidic group, the internal crosslinking agent, the polymerization initiator, and the neutralizing agent, at least some of the acidic groups of the water-soluble ethylenically unsaturated monomer may be neutralized. At this time, as the neutralizing agent, basic materials such as sodium hydroxide, potassium hydroxide, and ammonium hydroxide capable of neutralizing acidic groups may be used.

In addition, the degree of neutralization of the water-soluble ethylenically unsaturated monomer, which refers to the degree of neutralization by the neutralizing agent among the acidic groups included in the water-soluble ethylenically unsaturated monomer, is 50 to 90 mol%, or 60 to 85 mol%, or 65 to 85 mol% 85 mole %, or 65 to 75 mole %. The range of the degree of neutralization may vary depending on the final physical properties, but if the degree of neutralization is too high, neutralized monomers may be precipitated, making it difficult for the polymerization to proceed smoothly. It can exhibit properties like elastic rubber that are difficult to handle.

In addition, the term 'internal cross-linking agent' used herein is a term used to distinguish it from the surface cross-linking agent for cross-linking the surface of the superabsorbent polymer particles described later, and polymerization by cross-linking the unsaturated bonds of the above-described water-soluble ethylenically unsaturated monomers play a role in Crosslinking in this step proceeds regardless of surface or internal crosslinking, but when the surface crosslinking process of the superabsorbent polymer particles described later proceeds, the surface of the finally prepared superabsorbent polymer particles has a structure crosslinked by a surface crosslinking agent, The inside is made up of a cross-linked structure by the internal cross-linking agent.

As the internal crosslinking agent, any compound may be used as long as it enables the introduction of crosslinking bonds during polymerization of the water-soluble ethylenically unsaturated monomer. As a non-limiting example, the internal crosslinking agent is N, N'-methylenebisacrylamide, trimethylolpropane tri(meth)acrylate, ethylene glycol di(meth)acrylate, polyethylene glycol (meth)acrylate, polyethylene glycol di( Meth)acrylate, propylene glycol di(meth)acrylate, polypropylene glycol (meth)acrylate, butanediol di(meth)acrylate, butylene glycol di(meth)acrylate, diethylene glycol di(meth)acrylate Hexanediol di(meth)acrylate, triethylene glycol di(meth)acrylate, tripropylene glycol di(meth)acrylate, tetraethylene glycol di(meth)acrylate, dipentaerythritol pentaacrylate, glycerin tri Multifunctional crosslinking agents such as (meth)acrylate, pentaerythol tetraacrylate, triarylamine, ethylene glycol diglycidyl ether, propylene glycol, glycerin, or ethylene carbonate may be used alone or in combination of two or more. It is not limited. Preferably, among them, polyethylene glycol di(meth)acrylate may be used.

The cross-linking polymerization of the water-soluble ethylenically unsaturated monomer in the presence of such an internal cross-linking agent may be carried out by thermal polymerization, photo-polymerization or co-polymerization in the presence of a polymerization initiator and, if necessary, a thickener, a plasticizer, a storage stabilizer, an antioxidant, and the like. However, the specific details will be discussed later.

The superabsorbent polymer particles may have a particle size of about 150 to about 850 μm, and this particle size may be measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 220.3 method.

In addition, the second crosslinked polymer is formed by further crosslinking the crosslinked polymer on at least a portion of the surface of the base resin particle via a surface crosslinking agent, and the superabsorbent polymer particle is formed through a surface crosslinking layer containing the second crosslinked polymer. surface cross-linking density can be further increased. Accordingly, the superabsorbent polymer particle has a structure in which the crosslinking density is higher on the outside than on the inside.

As the surface crosslinking agent, any surface crosslinking agent conventionally used in the preparation of the superabsorbent polymer may be used without particular limitation. For example, the surface crosslinking agent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2- 1 selected from the group consisting of methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol more than one polyol; At least one carbonate-based compound selected from the group consisting of ethylene carbonate, propylene carbonate and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc. may be included.

Specifically, one or more, two or more, or three or more of the aforementioned surface crosslinking agents may be used as the surface crosslinking agent, and for example, an epoxy compound such as ethylene glycol diglycidyl ether may be used.

In addition, the super absorbent polymer includes at least two types of hydrophobic materials including a linear or branched hydrocarbon group having 11 or more carbon atoms, and these hydrophobic materials include sucrose acid ester, sorbitan fatty acid ester, and polyoxyethylene sorbitan fatty acid. It is selected from the group consisting of esters.

At this time, at least a portion of the hydrophobic material may be present on the surface of the superabsorbent polymer particle. Here, "at least a part of the hydrophobic material is present on the surface of the super absorbent polymer particle" means that at least a part of the hydrophobic material is adsorbed or bound to the surface of the super absorbent polymer particle. Specifically, the hydrophobic material may be physically or chemically adsorbed on the surface of the superabsorbent polymer. More specifically, the hydrophilic functional group of the hydrophobic material may be physically adsorbed to the hydrophilic portion of the surface of the superabsorbent polymer particle by intermolecular forces such as dipole-dipole interaction and hydrogen bonding. In this way, the hydrophilic functional group of the hydrophobic material is physically adsorbed on the surface of the super absorbent polymer particle to cover the surface, and the hydrophobic functional group of the hydrophobic material is not adsorbed on the surface of the super absorbent polymer particle, so that part of the surface of the super absorbent polymer particle may be coated with a hydrophobic functional group of a hydrophobic material.

Therefore, when at least a part of the hydrophobic material is present on the surface of the super absorbent polymer particle, even if the sanitary material made of the super absorbent polymer absorbs a large amount of liquid such as urine and swells, all of the hydrophobic material is the super absorbent polymer particle It is possible to more effectively improve the tactile feel of the superabsorbent polymer compared to the case where it is present inside, specifically, inside the crosslinked polymer.

Meanwhile, the superabsorbent polymer may not contain other hydrophilic and hydrophobic materials other than the hydrophobic material and hydrolyzate produced by hydrolysis of the hydrophobic materials during the manufacturing process of the superabsorbent polymer.

Here, the sucrose acid ester may be selected from sucrose stearate, sucrose palmitate and sucrose laurate.

In addition, the sorbitan fatty acid ester may be selected from sorbitan monostearate, sorbitan monopalmitate, and sorbitan monolaurate.

At this time, commercially available sorbitan fatty acid esters include SPAN ^® 60 (sorbitan monostearate), SPAN ^® 40 (sorbitan monopalmitate), or SPAN ^® 20 (sorbitan monolaurate). there is.

In addition, the polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monopalmitate and polyoxyethylene sorbitan monolaurate. monolaurate).

At this time, commercially available polyoxyethylene sorbitan fatty acid esters include TWEEN ^® 60 (polyoxyethylene (20) sorbitan monostearate; Polysorbate 60), TWEEN ^® 40 (polyoxyethylene (20) sorbitan monopalmi) Tate; Polysorbate 40), or TWEEN ^® 20 (polyoxyethylene (20) sorbitan monolaurate; Polysorbate 20) and the like.

Meanwhile, the superabsorbent polymer may include two types of hydrophobic materials, and each of the two types of hydrophobic materials may be selected from sucrose acid esters and sorbitan fatty acid esters. In other words, the first hydrophobic material may be sucrose acid ester, and the second hydrophobic material may be sorbitan fatty acid ester. When using two types of hydrophobic materials in such a combination, it may be preferable in that a more uniform hydrophobic treatment is possible when one type of hydrophobic material is used.

In addition, the sucrose acid ester and the sorbitan fatty acid ester may be included in a weight ratio of 1:1 to 1:2 in the superabsorbent polymer. If too little of the sorbitan fatty acid ester is used compared to the sucrose acid ester, there is a problem that sufficient hydrophobic treatment is not performed on the surface. It is undesirable because there is a possibility of deterioration.

In addition, the total weight of the hydrophobic material may be included in 0.005 to 0.05% by weight based on the total weight of the superabsorbent polymer. If the content of the hydrophobic material in the composition is too low, the hydrophobic effect of the super absorbent polymer particles by the hydrophobic material may not appear. Absorption rate may be reduced. At this time, the hydrophobic material may be detected in an amount lower than the actual input amount. This is because a significant portion of the hydrophobic material may be decomposed or volatilized during the drying process when the decomposition temperature of the hydrophobic material is lower than the drying temperature in the surface crosslinking process described later. am.

The content of the hydrophobic material in the superabsorbent polymer is determined by first adding 1 g of the superabsorbent polymer to 5 mL of Tetrahydrofuran, mixing thoroughly for 1 hour until the hydrophobic material is dissolved, centrifuging it, and filtering the supernatant. After extracting only the solution portion, HPLC-MS analysis is performed to analyze and measure the content of the hydrophobic substance dissolved in the solution portion.

In addition, the surface crosslinking agent and the hydrophobic material may be included in a weight ratio of 1:0.1 to 1:2. When the hydrophobic material is used in an excessively low content compared to the surface cross-linking agent, the surface does not exhibit sufficient hydrophobicity and there is a risk of deterioration of the touch. This is not preferable because the absorption rate of the superabsorbent polymer is lowered.

More specifically, the hydrophobic material is 0.1 times or more, 0.12 times or more, 0.14 times or more, 0.15 times or more, or 0.16 times or more, and 2 times or less, 1.9 times or less, 1.8 times or less, or 1.7 times, based on the weight of the surface crosslinking agent. It can be included in the following weight.

In addition, about 90% by weight, preferably at least 95% by weight of the superabsorbent polymer may be superabsorbent polymer particles having a particle diameter of about 150 to 850 μm, based on the total weight, and less than about 10% by weight, more specifically may be a fine powder having a particle diameter of less than about 5% by weight of less than about 150 μm.

In addition, the superabsorbent polymer has a water retention capacity (CRC) of 30 g/g or more, 31 g/g or more, or 32 g/g or more, and 40 g/g or less, or 35 It may have a range of g/g or less.

In addition, the superabsorbent polymer may have a vortex absorption rate of 60 seconds or less, 58 seconds or less, or 55 seconds or less by a vortex method at 24°C. In addition, the absorption rate is excellent as the value is small, and the lower limit of the absorption rate is 0 seconds in theory, but may be, for example, 45 seconds or more, or 50 seconds or more. In this case, a method for measuring the absorption rate of the superabsorbent polymer will be described in more detail in Examples to be described later.

In addition, the water-soluble component (Swollen SAP Surface Extractable Contents; SS E / C) on the surface of the swollen super-absorbent polymer measured according to the methods 1) to 3) below is 5% by weight or less based on the total weight of the super-absorbent polymer can:

1) putting 2.0 g of superabsorbent polymer in an Erlenmeyer flask, adding 50 g of a 0.9% by weight NaCl solution to the Erlenmeyer flask and swelling it for 1 hour;

2) adding 150 g of a 0.9% by weight NaCl solution to the Erlenmeyer flask, leaving it for 2 minutes, and then filtering the aqueous solution with filter paper; and

3) Measuring E/C (Extractable Contents) according to the EDANA method WSP 270.2 R2 method using 50 g of the solution filtered through the filter paper as a sample.

Here, the SS E/C measurement value is different from the general extractable content (E/C) measurement data. After swelling and leaving the super absorbent polymer without stirring, the value of the SS E/C escapes to the surface of the super absorbent polymer and affects the touch. It is a scale that can represent the touch of superabsorbent polymer swollen by a liquid such as urine by measuring only the components. At this time, the “water-soluble component (EC)” of the super absorbent polymer refers to a compound in the form of a polymer that is not crosslinked during the manufacturing process of the super absorbent polymer, and is not crosslinked due to incomplete crosslinking during polymerization, or chopping or In the drying process, the crosslinking agent may be decomposed or the main molecular chain may be broken. This water-soluble component is a problem because it can be easily eluted when the superabsorbent polymer absorbs liquid and swells. Therefore, as the value of the water-soluble component measured in the swollen superabsorbent polymer increases, the content of the component that is eluted increases, and the surface of the sanitary material such as a diaper may become sticky, resulting in poor tactile feel. In addition, the SS E / C measured above is excellent as the value is small, and the lower limit of the SS E / C is theoretically 0% by weight, but for example, 1% by weight or more, 5% by weight or more, or 10% by weight based on the total weight of the superabsorbent polymer may have a value greater than or equal to weight percent.

Manufacturing method of superabsorbent polymer

On the other hand, the superabsorbent polymer of one embodiment,

forming a water-containing gel polymer by cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal cross-linking agent and a polymerization initiator (Step 1);

drying and pulverizing the water-containing gel polymer to prepare a base resin (step 2); and

Forming a surface crosslinking layer on at least a part of the surface of the base resin by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent and two or more kinds of hydrophobic materials including a linear or branched hydrocarbon group having 11 or more carbon atoms. (step 3) is prepared,

Here, the hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters.

Hereinafter, a method for manufacturing a superabsorbent polymer according to an embodiment will be described in more detail for each step, but the description of the hydrophobic material will be referred to the above.

(Step 1)

In the method for preparing a super absorbent polymer according to an embodiment, first, a step of forming a water-containing gel polymer is performed by cross-linking and polymerizing a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal cross-linking agent and a polymerization initiator. .

The step may include preparing a monomer composition by mixing the water-soluble ethylenically unsaturated monomer, internal crosslinking agent, and polymerization initiator, and forming a hydrogel polymer by thermally or photopolymerizing the monomer composition. At this time, the description of the water-soluble ethylenically unsaturated monomer and the internal crosslinking agent refers to the above.

In the monomer composition, the internal crosslinking agent may be used in an amount of 0.01 to 5 parts by weight based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. For example, the internal crosslinking agent is 0.01 parts by weight or more, 0.05 parts by weight or more, or 0.1 parts by weight or more, based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer, and 5 parts by weight or less, 3 parts by weight or less, 2 parts by weight or less, 1 It may be used in parts by weight or less, or 0.7 parts by weight or less. If the content of the upper internal cross-linking agent is too low, cross-linking does not occur sufficiently, making it difficult to realize an appropriate level of strength. If the content of the upper internal cross-linking agent is too high, the internal cross-linking density increases, making it difficult to realize the desired water retention capacity.

In addition, the polymerization initiator may be appropriately selected according to the polymerization method, a thermal polymerization initiator is used when a thermal polymerization method is used, a photopolymerization initiator is used when a photopolymerization method is used, and a hybrid polymerization method (thermal and photopolymerization initiators) is used. In the case of using both), both a thermal polymerization initiator and a photopolymerization initiator may be used. However, even with the photopolymerization method, since a certain amount of heat is generated by light irradiation such as ultraviolet irradiation, and a certain amount of heat is generated as the polymerization reaction progresses, which is an exothermic reaction, a thermal polymerization initiator may be additionally used.

As the photopolymerization initiator, any compound capable of forming radicals by light such as ultraviolet light may be used without limitation in its configuration.

Examples of the photopolymerization initiator include benzoin ether, dialkyl acetophenone, hydroxyl alkylketone, phenyl glyoxylate, and benzyl dimethyl ketal. Ketal), acyl phosphine, and alpha-aminoketone (α-aminoketone) may be used at least one selected from the group consisting of. On the other hand, specific examples of acylphosphine include diphenyl (2,4,6-trimethylbenzoyl) phosphine oxide, phenylbis (2,4,6-trimethylbenzoyl) phosphine oxide, ethyl (2,4,6- Trimethylbenzoyl) phenylphosphinate etc. are mentioned. More various photoinitiators are well described in "UV Coatings: Basics, Recent Developments and New Application (Elsevier 2007)" p115, a book by Reinhold Schwalm, and are not limited to the above examples.

In addition, as the thermal polymerization initiator, at least one selected from the group consisting of a persulfate-based initiator, an azo-based initiator, hydrogen peroxide, and ascorbic acid may be used. Specifically, examples of persulfate-based initiators include sodium persulfate (Na ₂ S ₂ O ₈ ), potassium persulfate (K ₂ S ₂ O ₈ ), and ammonium persulfate ((NH ₄ ) ₂ S ₂ O ₈ ) and the like, and examples of the azo-based initiator include 2,2-azobis-(2-amidinopropane) dihydrochloride, 2 ,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride (2,2-azobis-(N,N-dimethylene)isobutyramidine dihydrochloride), 2-(carbamoyl azo)isobutyronitrile (2-(carbamoylazo)isobutylonitril), 2,2-azobis[2-(2-imidazolin-2-yl)propane] dihydrochloride (2,2-azobis[2-(2-imidazolin-2- yl)propane] dihydrochloride) and 4,4-azobis-(4-cyanovaleric acid). More various thermal polymerization initiators are well described in Odian's 'Principle of Polymerization (Wiley, 1981)', p203, and are not limited to the above examples.

The polymerization initiator may be used in an amount of 2 parts by weight or less based on 100 parts by weight of the water-soluble ethylenically unsaturated monomer. That is, when the concentration of the polymerization initiator is too low, the polymerization rate may be slowed and a large amount of residual monomer may be extracted into the final product, which is not preferable. Conversely, when the concentration of the polymerization initiator is higher than the above range, the polymer chain constituting the network is shortened, which is not preferable because the physical properties of the resin may be deteriorated, such as an increase in the content of water-soluble components and a decrease in absorbency under pressure.

The monomer composition may further include a hydrophobic material such as a thickener, a plasticizer, a storage stabilizer, and an antioxidant, if necessary.

And, the monomer composition including the monomer may be, for example, in a solution state dissolved in a solvent such as water, and the solid content, that is, the concentration of the monomer, the internal crosslinking agent, and the polymerization initiator in the monomer composition in the solution state is determined by polymerization. It may be appropriately adjusted in consideration of time and reaction conditions. For example, the solids content in the monomer composition may be 10 to 80% by weight, or 15 to 60% by weight, or 30 to 50% by weight.

When the monomer composition has a solid content in the above range, the gel effect phenomenon that occurs in the polymerization reaction of a high-concentration aqueous solution is used to eliminate the need to remove unreacted monomers after polymerization, while increasing the pulverization efficiency when pulverizing the polymer, which will be described later. It can be advantageous to adjust.

The solvent that can be used at this time can be used without limitation in composition as long as it can dissolve the above-mentioned components. For example, water, ethanol, ethylene glycol, diethylene glycol, triethylene glycol, 1,4-butanediol, propylene Glycol, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, propylene glycol monomethyl ether acetate, methyl ethyl ketone, acetone, methyl amyl ketone, cyclohexanone, cyclopentanone, diethylene glycol monomethyl ether, diethylene glycol ethyl At least one selected from ether, toluene, xylene, butyrolactone, carbitol, methylcellosolveacetate, and N,N-dimethylacetamide may be used in combination.

On the other hand, cross-linking polymerization of water-soluble ethylenically unsaturated monomers having at least partially neutralized acidic groups can be carried out without any particular limitation in configuration, as long as a water-containing gel polymer can be formed by thermal polymerization, photopolymerization, or co-polymerization.

Specifically, the polymerization method is largely divided into thermal polymerization and photopolymerization according to the polymerization energy source. In the case of normal thermal polymerization, it can be carried out in a reactor having an agitation shaft such as a kneader, and in the case of photopolymerization, a movable It may be carried out in a reactor equipped with a conveyor belt or in a container with a flat bottom, but the above polymerization method is an example, and the present invention is not limited to the above polymerization method.

For example, as described above, the water-containing gel polymer obtained by thermal polymerization by supplying hot air to a reactor such as a kneader equipped with an agitation shaft or heating the reactor is directed to the outlet of the reactor according to the shape of the agitation shaft provided in the reactor. The discharged water-containing gel polymer may be in the form of several centimeters to several millimeters. Specifically, the size of the obtained water-containing gel polymer may vary depending on the concentration and injection speed of the monomer composition to be injected, and a water-containing gel polymer having a weight average particle diameter of 2 to 50 mm can be obtained.

In addition, as described above, when photopolymerization is performed in a reactor equipped with a movable conveyor belt or in a container with a flat bottom, the form of a water-containing gel polymer that is usually obtained may be a sheet-like water-containing gel polymer having the width of a belt. At this time, the thickness of the polymer sheet varies depending on the concentration and injection rate or amount of the monomer composition to be injected, but it is preferable to supply the monomer composition so that a polymer sheet having a thickness of about 0.5 to about 5 cm can be obtained. do. When the monomer composition is supplied to such an extent that the thickness of the polymer on the sheet is too thin, production efficiency is low, which is undesirable. When the thickness of the polymer on the sheet exceeds 5 cm, the polymerization reaction does not occur evenly over the entire thickness due to the excessively thick thickness. may not be

In this case, the water-containing gel polymer obtained in this way may have a moisture content of 40 to 80% by weight. For example, the moisture content of the water-containing gel polymer may be 40 wt% or more, 45 wt% or more, 50 wt% or more, 55 wt% or more, 80 wt% or less, 77 wt% or less, or 75 wt% or less. If the water content of the water-containing gel polymer is too low, it is difficult to secure an appropriate surface area in the subsequent grinding step, and drying efficiency may be reduced. Absorption capacity may be lowered, and there is a concern that a lot of energy and a long time are required in the drying step after grinding. In addition, even when the water-containing gel polymer has a high moisture content such as 70% to 80% by weight, it is possible to pulverize the water-containing gel polymer without aggregation of the pulverized particles due to the above-described hydrophobic material.

Meanwhile, throughout the present specification, "moisture content" refers to a value obtained by subtracting the weight of the dry polymer from the weight of the hydrogel polymer as the content of moisture with respect to the total weight of the hydrogel polymer. Specifically, it is defined as a value calculated by measuring the weight loss due to moisture evaporation in the polymer during the drying process by raising the temperature of the polymer in the crumb state through infrared heating. At this time, the drying condition is a method of raising the temperature from room temperature to about 180 ° C and then maintaining it at 180 ° C. The total drying time is set to 40 minutes including 5 minutes of the temperature raising step, and the moisture content is measured.

(Step 2)

Next, a step of drying and pulverizing the water-containing gel polymer to form a base resin in a powder form is performed. If necessary, a step of coarsely pulverizing may be further performed before drying to increase the efficiency of the drying step.

At this time, the grinder used for coarse grinding is not limited in configuration, but specifically, a vertical pulverizer, a turbo cutter, a turbo grinder, a rotary cutting grinder ( Rotary cutter mill), cutter mill, disc mill, shred crusher, crusher, chopper and disc cutter It may include any one selected, but is not limited to the above-described examples.

At this time, in the coarsely pulverizing step, the polymer may be pulverized to have a particle size of about 2 to about 10 mm. Specifically, grinding to a particle diameter of less than 2 mm is not technically easy due to the high water content of the hydrogel polymer, and also a phenomenon in which the pulverized particles may aggregate with each other may occur. On the other hand, when grinding with a particle diameter of more than 10 mm, the effect of increasing the efficiency of the subsequent drying step is insignificant.

Drying is performed on the polymer immediately after polymerization that is pulverized as described above or not subjected to the pulverization step. At this time, the drying temperature of the drying step may be about 150 to about 250 ℃. When the drying temperature is less than 150 ° C, the drying time is too long and there is a risk of deterioration in the physical properties of the finally formed super absorbent polymer, and when the drying temperature exceeds 250 ° C, only the surface of the polymer is excessively dried, resulting in a subsequent pulverization process There is a concern that fine powder may be generated in the water, and physical properties of the finally formed superabsorbent polymer may be deteriorated. Therefore, preferably, the drying may be performed at a temperature of about 150 to about 200 °C, more preferably at a temperature of about 160 to about 180 °C.

Meanwhile, the drying time may be about 20 to about 90 minutes in consideration of process efficiency, but is not limited thereto.

The drying method of the drying step may be selected and used without any limitation in configuration, as long as it is commonly used as a drying process for hydrogel polymers. Specifically, the drying step may be performed by a method such as hot air supply, infrared ray irradiation, microwave irradiation, or ultraviolet ray irradiation. The moisture content of the polymer after such a drying step may be about 5 to about 10% by weight.

Next, a step of pulverizing the dried polymer obtained through such a drying step is performed.

The base resin, which is a polymer powder obtained after the grinding step, may have a particle size of about 150 to about 850 μm. The grinder used for grinding to such a particle size is specifically, a pin mill, a hammer mill, a screw mill, a roll mill, a disc mill, or a jog mill. A jog mill or the like may be used, but the present invention is not limited to the above examples.

In addition, in order to manage physical properties of the superabsorbent polymer powder to be finalized after the pulverization step, the base resin obtained after pulverization is classified according to the particle size. Preferably, a polymer having a particle diameter of about 150 to about 850 μm may be classified, and a surface crosslinking reaction step may be performed only for a base resin having such a particle diameter.

(Step 3)

Next, the surface of the base resin is additionally crosslinked in the presence of a surface crosslinking agent and two or more types of hydrophobic materials including a linear or branched hydrocarbon group having 11 or more carbon atoms to form a surface crosslinking layer on at least a part of the surface of the base resin. step is performed. Through the above step, the surface cross-linked layer including the second cross-linked polymer in which the first cross-linked polymer is additionally cross-linked on the surface of the base resin, more specifically, on at least a portion of the surface of each of the base resin particles through a surface cross-linking agent. The formed superabsorbent polymer is prepared.

The surface crosslinking is a step of increasing the crosslinking density near the surface of the superabsorbent polymer particle in relation to the crosslinking density inside the particle. Generally, a surface crosslinking agent is applied to the surface of a base resin. Accordingly, this reaction takes place on the surface of the superabsorbent polymer particles, which improves the crosslinkability on the surface of the particles without substantially affecting the inside of the particles. Therefore, the surface cross-linked superabsorbent polymer particles have a higher degree of cross-linking in the vicinity of the surface than in the inside.

As the surface crosslinking agent, any surface crosslinking agent conventionally used in the preparation of the superabsorbent polymer may be used without particular limitation. For example, the surface crosslinking agent is ethylene glycol, propylene glycol, 1,3-propanediol, 1,4-butanediol, 1,6-hexanediol, 1,2-hexanediol, 1,3-hexanediol, 2- 1 selected from the group consisting of methyl-1,3-propanediol, 2,5-hexanediol, 2-methyl-1,3-pentanediol, 2-methyl-2,4-pentanediol, tripropylene glycol and glycerol more than one polyol; At least one carbonate-based compound selected from the group consisting of ethylene carbonate, propylene carbonate and glycerol carbonate; epoxy compounds such as ethylene glycol diglycidyl ether; oxazoline compounds such as oxazolidinone; polyamine compounds; oxazoline compounds; mono-, di- or polyoxazolidinone compounds; or cyclic urea compounds; etc. may be included.

For example, it is preferable to use ethylene glycol diglycidyl ether as the surface crosslinking agent. These ethylene glycol diglycidyl ethers are highly water-soluble and have two epoxy groups, so surface reactions can easily proceed even at relatively low temperatures.

The content of the surface crosslinking agent may be appropriately selected depending on the type of surface crosslinking agent added or reaction conditions, but is about 0.001 to about 5 parts by weight, preferably about 0.01 to about 3 parts by weight, based on 100 parts by weight of the base resin. parts, more preferably from about 0.05 to about 2 parts by weight. If the content of the surface crosslinking agent is too small, surface crosslinking reaction hardly occurs, and if it exceeds 5 parts by weight with respect to 100 parts by weight of the base resin, excessive surface crosslinking reaction may cause deterioration in water absorption properties such as water retention capacity. there is.

The two or more hydrophobic materials may be used in an amount of 0.01 part by weight to 0.05 part by weight based on 100 parts by weight of the base resin. When the hydrophobic material is used in an amount of less than 0.01 parts by weight based on 100 parts by weight of the base resin, the hydrophobic effect of the superabsorbent polymer particles may not appear, and the hydrophobic material is used in an amount exceeding 0.05 parts by weight based on 100 parts by weight of the base resin. In this case, the water absorption rate of the super absorbent polymer may decrease because the hydrophobic material may interfere with the super absorbent polymer particles absorbing water.

In addition, the above two or more hydrophobic materials may be added to a surface crosslinking solution to be described later. The hydrophobic material may be dissolved or suspended by a solvent in the surface crosslinking solution.

In addition, the surface crosslinking agent and the two or more hydrophobic materials may be used in a weight ratio of 1:0.1 to 1:2. When the hydrophobic material is used in an excessively low content compared to the surface cross-linking agent, the surface does not exhibit sufficient hydrophobicity and there is a risk of deterioration of the touch. This is not preferable because the absorption rate of the superabsorbent polymer is lowered.

More specifically, the hydrophobic material is 0.1 times or more, 0.12 times or more, 0.14 times or more, 0.15 times or more, or 0.16 times or more, and 2 times or less, 1.9 times or less, 1.8 times or less, or 1.7 times, based on the weight of the surface crosslinking agent. The following weights can be used.

In addition, the forming of the surface cross-linking layer may be performed using an inorganic material together with the surface cross-linking agent. That is, in the presence of the surface crosslinking agent, the hydrophobic material, and the inorganic material, the surface of the base resin may be additionally crosslinked to form a surface crosslinking layer.

As the inorganic material, at least one inorganic material selected from the group consisting of silica, clay, alumina, silica-alumina composite, titania, zinc oxide, and aluminum sulfate may be used. The inorganic material may be used in powder form or liquid form. In addition, the inorganic material may be used in an amount of about 0.001 to about 1 part by weight based on 100 parts by weight of the base resin.

There is no limitation of the structure about the method of mixing the said surface crosslinking agent with base resin. A method of mixing the surface crosslinking agent and the base resin powder in a reaction tank, spraying the surface crosslinking agent on the base resin powder, or continuously supplying and mixing the base resin and the surface crosslinking agent to a continuously operated mixer may be used.

When adding the surface crosslinking agent, water may be mixed together and added in the form of a surface crosslinking solution. When water is added, there is an advantage that the surface crosslinking agent can be evenly dispersed in the polymer. At this time, the amount of water added is about 1 to 100 parts by weight of the base resin for the purpose of inducing uniform dispersion of the surface crosslinking agent, preventing agglomeration of the polymer powder, and at the same time optimizing the surface penetration depth of the surface crosslinking agent It is preferably added in a proportion of about 10 parts by weight.

When mixing the surface crosslinking agent and the superabsorbent polymer composition, water and methanol may be additionally mixed and added. When water and methanol are added, there is an advantage in that the surface crosslinking agent can be evenly dispersed in the superabsorbent polymer composition. At this time, the amounts of added water and methanol may be appropriately adjusted to induce uniform dispersion of the surface crosslinking agent, prevent agglomeration of the superabsorbent polymer composition, and optimize the surface penetration depth of the crosslinking agent.

The surface cross-linking reaction is performed by heating the base resin to which the surface cross-linking solution containing the surface cross-linking agent and the solvent is added at a temperature of about 100 to about 150 ° C. for about 15 to about 80 minutes, preferably about 20 to about 70 minutes. It can be done. If the crosslinking reaction temperature is less than 100 °C, the surface crosslinking reaction may not sufficiently occur, and if it exceeds 150 °C, the surface crosslinking density may increase and the absorption capacity may significantly decrease.

In addition, the means for raising the temperature for the surface crosslinking reaction is not particularly limited. It can be heated by supplying a heat medium or directly supplying a heat source. At this time, as the type of heat medium that can be used, steam, hot air, heated fluids such as hot oil, etc. can be used, but the present invention is not limited thereto, and the temperature of the heat medium supplied depends on the means of the heat medium, the rate of temperature increase and the temperature rise. It can be selected appropriately in consideration of the target temperature. On the other hand, as the directly supplied heat source, heating through electricity or heating through gas may be mentioned, but the present invention is not limited to the above-described examples.

As described above, after forming the surface crosslinking layer on the surface of the base resin, an inorganic material may be additionally mixed.

The inorganic material may be, for example, at least one selected from the group consisting of silica, clay, alumina, a silica-alumina composite, and titania, and preferably silica.

These inorganic materials may be used in an amount of 0.01 parts by weight or more, or 0.05 parts by weight or more, or 0.1 parts by weight or more, and 5 parts by weight or less, or 3 parts by weight or less, or 1 part by weight or less, based on 100 parts by weight of the superabsorbent polymer. can

Meanwhile, in order to manage physical properties of the super absorbent polymer to be finalized, a step of classifying the super absorbent polymer obtained after the surface crosslinking reaction according to the particle size may be additionally performed. Preferably, polymers having particle diameters of about 150 to about 850 μm are classified, and only superabsorbent polymers having such particle diameters can be used as final products.

Hereinafter, preferred embodiments are presented to aid understanding of the invention. However, the following examples are only for exemplifying the invention and are not intended to limit the invention only to these.

Example - Preparation of Super Absorbent Polymer

Example 1

(Step 1) In a 3L glass container equipped with a stirrer and a thermometer, 100 g (1.388 mol) of acrylic acid, 0.16 g of internal crosslinking agent polyethylene glycol diacrylate (Mn = 508), and photopolymerization initiator diphenyl (2, 4,6-trimethylbenzoyl 0.008 g of phosphine oxide, 0.12 g of thermal polymerization initiator sodium persulfate, and 123.5 g of 32% caustic soda solution were mixed at room temperature to prepare a monomer composition (degree of neutralization of acrylic acid: 70 mol%, solid content: 45% by weight) ).

Thereafter, the monomer composition was supplied at a speed of 500 to 2000 mL/min on a conveyor belt in which a belt having a width of 10 cm and a length of 2 m rotated at a speed of 50 cm/min. And, simultaneously with the supply of the monomer composition, UV light having an intensity of 10 mW/cm ² was irradiated to conduct a polymerization reaction for 60 seconds, thereby obtaining a water-containing gel polymer having a water content of 55% by weight.

(Step 2) Next, the hydrophobic material solution prepared in Preparation Example 1 was mixed with the water-containing gel polymer obtained through the polymerization reaction so that 1 part by weight of the first hydrophobic material was added to 100 parts by weight of the water-containing gel polymer. , It was pulverized into particles having a particle diameter of 150 μm to 850 μm using a meat chopper equipped with a perforated plate having a plurality of cut holes with a diameter of 1 mm. At this time, the pulverized product contained 80% by weight of pulverized water-containing gel polymer particles having a particle size of 250 μm or less.

Thereafter, the pulverized product is dried by flowing hot air at 185 ° C. from bottom to top for 20 minutes using a rotary (flow type) oven capable of transferring air volume up and down, and then flowing from top to bottom for another 20 minutes. , the base resin was prepared.

(Step 3) Next, 5.0 g of water, 3.0 g of methanol, 0.06 g of ethylene glycol diglycidyl ether (EJ1030s) as a surface crosslinking agent, 0.3 g of 23% aluminum sulfate aqueous solution, and two types of hydrophobicity were added to 100 g of the obtained base resin. After adding 0.005 g of sucrose stearate (S-570, manufactured by Mitsubishi chemical) and 0.005 g of polyoxyethylene (20) sorbitan monolaurate (SPAN ^® 20, manufactured by Sigma-Aldrich), minutes, and dried at 140° C. for 40 minutes to prepare a final superabsorbent polymer.

Examples 2 to 4

A superabsorbent polymer was prepared in the same manner as in Example 1, except that the hydrophobic material in Table 2 was used instead of the hydrophobic material in Example 1.

Reference Example 1

A superabsorbent polymer was prepared in the same manner as in Example 1, except that one hydrophobic material in Table 2 was used instead of the two hydrophobic materials in Example 1.

Comparative Example 1

A superabsorbent polymer was prepared in the same manner as in Example 1, except that the hydrophobic material was not used in Example 1 (Step 3).

Comparative Examples 2 to 5

A superabsorbent polymer was prepared in the same manner as in Example 1, except that one hydrophobic material in Table 2 was used instead of the two hydrophobic materials in Example 1.

Test Example 1

With respect to the superabsorbent polymers prepared in Example 1 and Comparative Example 1, the hydrophobic material content contained therein was measured in the following manner, respectively, and the results are shown in Table 1 below.

1) After putting 1 g of the finally prepared superabsorbent polymer into 5 mL of tetrahydrofuran, the mixture was sufficiently mixed for 1 hour until the hydrophobic material on the surface was dissolved.

2) After centrifuging the mixture, the supernatant was filtered to extract only the solution portion, and then the hydrophobic material content dissolved in the solution portion was quantified through HPLC-MS analysis.

Type of hydrophobic material
(content) ¹⁾ Example 1 sucrose stearate
(0.004% by weight) Sorbitan Monolaurate
(0.004% by weight) Comparative Example 1 - -

1) Weight based on total weight of superabsorbent polymer

test example 2

With respect to the superabsorbent polymers prepared in the above Examples and Comparative Examples, centrifugal water retention capacity (CRC), absorption rate, and SS E/C were respectively measured in the following manner, and the results are shown in Table 2 below. Unless otherwise indicated, the following physical property evaluation was carried out in a constant temperature and humidity room (23 ± 2 ℃, relative humidity 45 ± 10%), and the average value of three measurements was used as the measurement data to prevent measurement errors. In addition, in the evaluation of physical properties below, physiological saline or saline means a 0.9% by weight aqueous solution of sodium chloride (NaCl).

(1) Centrifuge Retention Capacity (CRC)

The water retention capacity of each resin composition under no load under water absorption was measured according to the European Disposables and Nonwovens Association (EDANA) standard EDANA WSP 241.3.

Specifically, from the resin compositions obtained through Examples and Comparative Examples, resin compositions classified through a #30-50 sieve were obtained. This resin composition W ₀ (g) (about 0.2 g) was uniformly placed in a bag made of nonwoven fabric and sealed, and then immersed in physiological saline (0.9% by weight) at room temperature. After 30 minutes, water was drained from the bag for 3 minutes under the condition of 250 G using a centrifuge, and the mass W ₂ (g) of the bag was measured. Moreover, after carrying out the same operation without using resin, the mass _W1 (g) at that time was measured.

CRC (g/g) was calculated according to Equation 1 below using each mass obtained.

[Equation 1]

CRC (g/g) = {[W ₂ (g) - W ₁ (g)]/W ₀ (g)} - 1

(2) Absorption rate (Vortex time)

The absorption rate (vortex time) of the superabsorbent polymers of Examples and Comparative Examples was measured in the following manner.

① First, 50 mL of 0.9% saline was added to a 100 mL beaker with a flat bottom using a 100 mL Mass Cylinder.

② Next, after placing the beaker in the center of the magnetic stirrer, a circular magnetic bar (30 mm in diameter) was placed in the beaker.

③ Then, the stirrer was operated so that the magnetic bar was stirred at 600 rpm, and the lowest part of the vortex generated by the stirring was brought into contact with the top of the magnetic bar.

④ After confirming that the temperature of the brine in the beaker has reached 24.0℃, insert 2±0.01 g of the superabsorbent polymer sample and simultaneously operate the stop watch. It was measured as a unit, and this was taken as the absorption rate.

(3) Water-soluble components on the surface of the swollen superabsorbent polymer (SS E/C)

SS E/C of the superabsorbent polymers of Examples and Comparative Examples was measured in the following manner.

① First, 2.0 g of the superabsorbent polymer was placed in an Erlenmeyer flask, and 50 g of a 0.9% by weight NaCl solution was added to the Erlenmeyer flask, followed by swelling for 1 hour.

② Next, 150 g of 0.9% by weight NaCl solution was additionally added to the Erlenmeyer flask, left for 2 minutes, and then the aqueous solution was filtered with filter paper.

③ Then, E / C (Extractable Contents) was measured according to the EDANA method WSP 270.2 R2 method using 50 g of the solution filtered through the filter paper as a sample.

hydrophobic material
(content ¹⁾ ) SAP properties CRC
(g/g) absorption rate
(candle) SS E/C
(weight %) Example
One sucrose
stearate
(0.005) Sorbitan
monolaurate
(0.005) 32.3 53 4.9 Example
2 sucrose
stearate
(0.015) Sorbitan
monolaurate
(0.015) 32.2 54 4.6 Example
3 sucrose
stearey
Bit (0.025) Sorbitan
monolaurate
(0.025) 32.3 55 4.5 Example
4 sucrose
stearate
(0.01) Sorbitan
monolaurate
(0.02) 32.2 55 4.7 reference example
One sucrose
stearate
(0.05) Sorbitan
monolaurate
(0.05) 32.0 58 4.5 comparative example
One - 32.3 52 7.0 comparative example
2 sucrose stearate
(0.01) 32.2 52 6.6 comparative example
3 sucrose stearate
(0.03) 32.4 53 6.5 comparative example
4 sucrose stearate
(0.05) 32.2 54 6.3 comparative example
5 Sorbitan Monolaurate
(0.05) 32.1 54 6.4

1) parts by weight relative to 100 parts by weight of the base resin

Referring to Table 2, when a superabsorbent polymer is prepared by using two types of hydrophobic materials together in the surface crosslinking process, compared to the case of using only the hydrophobic material or not using such a hydrophobic material, the absorption performance and It can be seen that the tactile feel of the super absorbent polymer after swelling was improved because the content of water-soluble components on the surface of the super absorbent polymer after swelling was low without a decrease in absorption rate.

Claims (11)

A base resin comprising a first crosslinked polymer of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized, and a second crosslinked polymer formed on the base resin and further crosslinked with a surface crosslinking agent. superabsorbent polymer particles including a surface crosslinking layer containing a crosslinked polymer; and
Contains two or more hydrophobic substances containing a linear or branched hydrocarbon group having 11 or more carbon atoms,
The hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters,
super absorbent polymer.
According to claim 1,
At least a portion of the hydrophobic material is present on the surface of the superabsorbent polymer particle,
super absorbent polymer.
According to claim 1,
The sucrose acid ester is selected from sucrose stearate, sucrose palmitate and sucrose laurate,
super absorbent polymer.
According to claim 1,
The sorbitan fatty acid ester is selected from sorbitan monostearate, sorbitan monopalmitate and sorbitan monolaurate,
super absorbent polymer.
According to claim 1,
The polyoxyethylene sorbitan fatty acid ester is polyoxyethylene sorbitan monostearate, polyoxyethylene sorbitan monopalmitate and polyoxyethylene sorbitan monolaurate. selected from,
super absorbent polymer.
According to claim 1,
The superabsorbent polymer includes two types of hydrophobic materials,
The two hydrophobic materials are each selected from sucrose acid esters and sorbitan fatty acid esters,
super absorbent polymer.
According to claim 6,
The sucrose acid ester and the sorbitan fatty acid ester are included in a weight ratio of 1: 1 to 1: 2,
super absorbent polymer.
According to claim 1,
In the superabsorbent polymer, the water-soluble component (Swollen SAP Surface Extractable Contents; SS E / C) on the surface of the swollen superabsorbent polymer measured according to the methods 1) to 3) below is 5% by weight or less based on the total weight of the superabsorbent polymer.
1) putting 2.0 g of the superabsorbent polymer in an Erlenmeyer flask, adding 50 g of a 0.9% by weight NaCl solution to the Erlenmeyer flask, and then swelling the Erlenmeyer flask for 1 hour;
2) adding 150 g of a 0.9% by weight NaCl solution to the Erlenmeyer flask, leaving it for 2 minutes, and then filtering the aqueous solution with filter paper; and
3) Measuring E/C (Extractable Contents) according to the EDANA method WSP 270.2 R2 method using 50 g of the solution filtered through the filter paper as a sample.
forming a water-containing gel polymer by cross-linking polymerization of a water-soluble ethylenically unsaturated monomer having an acidic group at least partially neutralized in the presence of an internal cross-linking agent and a polymerization initiator (Step 1);
drying and pulverizing the water-containing gel polymer to prepare a base resin (step 2); and
Forming a surface crosslinking layer on at least a part of the surface of the base resin by further crosslinking the surface of the base resin in the presence of a surface crosslinking agent and two or more kinds of hydrophobic materials including a linear or branched hydrocarbon group having 11 or more carbon atoms. (step 3),
The hydrophobic material is selected from the group consisting of sucrose acid esters, sorbitan fatty acid esters and polyoxyethylene sorbitan fatty acid esters,
A method for producing a superabsorbent polymer.
According to claim 9,
The two or more hydrophobic materials are used in an amount of 0.01 part by weight to 0.05 part by weight based on 100 parts by weight of the base resin.
A method for producing a superabsorbent polymer.
According to claim 9,
The surface crosslinking agent and the two or more hydrophobic materials are used in a weight ratio of 1:0.1 to 1:2,
A method for producing a superabsorbent polymer.